Lateral semiconductor device with maximized breakdown voltage, and methods of fixing potential of same

Abstract

A lateral semiconductor device with enhanced breakdown characteristics includes a semiconductor substrate composite of first and second semiconductor substrates bonded to one another via an oxide film. An insulation film is buried in a separation trench which extends from a major surface of the first semiconductor substrate to the oxide film. An element region of greater than 10 μm in thickness is isolated by the separation trench from other element regions. First and second diffusion regions of opposite conductivity type are formed on the element region. The potential of the second substrate is fixed at one-third of the designed maximum breakdown voltage of the lateral semiconductor device. Alternatively, if the element region is 10 μm or less in thickness, the potential of the second substrate is fixed at one-half of the designed maximum breakdown voltage of the lateral semiconductor device.

I claim: 
     
       1. A method of fixing the potential of a lateral semiconductor device, said lateral semiconductor device including a semiconductor substrate composite having a maximum breakdown voltage and first and second semiconductor substrates mutually bonded to an oxide film, wherein said first semiconductor substrate comprises an element region which has a thickness less than or equal to 10 μm and which is isolated from other element regions by an insulator region extending from a major surface of said first semiconductor substrate to said oxide film, a first diffusion region of a first conductivity type disposed on said element region, and a second diffusion region of a second conductivity type also disposed on said element region, said method comprising the step of fixing said second substrate at a potential which is one-half of said maximum breakdown voltage. 
     
     
       2. The method of claim 1, wherein the element region has a minimum potential, wherein the insulator region in part consists of polycrystalline silicon, and wherein the method further comprises fixing the polycrystalline silicon at a potential bias higher than the minimum potential of the element region. 
     
     
       3. The method of claim 2, wherein the potential bias of the polycrystalline silicon equals second-semiconductor-substrate potential. 
     
     
       4. A method of fixing the potential of a lateral semiconductor device, said lateral semiconductor device including a semiconductor substrate composite having a maximum breakdown voltage and first and second semiconductor substrates mutually bonded to an oxide film, wherein said first semiconductor substrate comprises an element region which has a thickness greater than 10 μm and which is isolated from other element regions by an insulator region extending from a major surface of said first semiconductor substrate to said oxide film, a first diffusion region of a first conductivity type disposed on said element region, a second diffusion region of a second conductivity type also disposed on said element region, said method comprising the step of fixing said second substrate at a potential which is one-third of said maximum breakdown voltage. 
     
     
       5. The method of claim 4, wherein the element region has a minimum potential, wherein the insulator region in part consists of polycrystalline silicon, and wherein the method further comprises fixing the polycrystalline silicon at a potential bias higher than the minimum potential of the element region. 
     
     
       6. The method of claim 5, wherein the potential bias of the polycrystalline silicon equals second-semiconductor-substrate potential.